For checking the luminescence radiation, such as phosphorescence or fluorescence radiation, emanating from a value document it is customary to use systems as are described by way of example in DE 23 66 274 C2. Accordingly, a bank note to be checked is irradiated with light and the remitted luminescence radiation detected with spectral resolution to determine whether a luminescent feature substance is actually contained in the bank note to be checked.
A luminescent feature substance is understood to be a substance comprising a single component or a mixture of several components that show luminescence behavior. Said feature substances, which can be present e.g. in the form of pigments, are contained in the value document itself and/or applied thereto. The feature substances can e.g. also be applied in spatially coded form to permit different nominal values of a currency system to be distinguished.
To make it more difficult for forgers to produce forged bank notes, an attempt is made to maintain secrecy on information about the exact composition and the characteristic spectral properties of the luminescent feature substances which are measured by the luminescence sensors.
A time-tested concept for maintaining secrecy on said information is that the associated luminescence sensors must also be so secured as not to transmit any measuring values outwardly.
For this purpose, the luminescence sensor with its evaluation electronics is e.g. mounted in a closed housing secured from access. The evaluation electronics is used for evaluating the recorded measuring values. The result of evaluation of the particular bank note can consist e.g. in a classification of the bank note into one of the categories, “authentic,” “false,” “suspect,” or “non-recognized” bank note.
The housing has an interface for transmitting data to an external unit, such as a control unit of an automatic teller machine or a bank note sorting apparatus in which the luminescence sensor is integrated. The control unit is normally connected to a display which displays, i.e. visually represents, information about the result of the check to the operator of the automatic teller machine or bank note sorting apparatus. The transmission of data to an external unit, such as a downstream data evaluation unit or the display of a quality control device used for quality testing of the bank note in or after its production, is of special interest. Particularly in this case it is of interest or even necessary to provide the user with information about the feature in addition to the intensity of the feature, so that production can be carried out within given tolerances. Alternatively, production can also be followed by a check of given tolerances, which evaluates more than only e.g. the intensity of the luminescent substance.
What is essential is that no measuring data are transmitted to the external unit via the interface of the luminescence sensor. Only the classification results themselves (authentic, false, suspect, non-recognized bank note) are relayed from the bank note sensor to the external unit and displayed.
Since an authorized or also unauthorized user of the luminescence sensor thus fundamentally obtains no information about the actual measuring values of the bank notes, no conclusions can be drawn on the luminescent feature substances. This permits the secrecy of information about the luminescent feature substances to be reliably ensured.
However, there are now also luminescence sensors for bank notes that are equipped with an analog interface for relaying measuring values of the measured luminescence radiation to an external unit. For quality control during papermaking or bank note production, graphic representations of the spectral curves themselves are then displayed on a screen of the external unit.
Thus, persons using the luminescence sensors can obtain from the visual representation information about the measuring values themselves or quantities derived therefrom, e.g. about the measured spectral curves of the luminescent feature substances. This permits conclusions to be drawn on the luminescent feature substances, which can in principle also be used improperly for copying the feature substances.
On these premises, it is the problem of the present invention to provide an apparatus and method for visually representing measuring values, in particular in the check of value documents, which avoid the above-mentioned disadvantages.